The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Unmanned Aerial Vehicles (UAVs), alternatively Unmanned Air Vehicles, are growing in importance for both military and non-military applications. UAVs typically make use of an on-board antenna, and more typically an omnidirectional on-board antenna, to wirelessly transmit information back to a ground station or base station. Typically, extra power is used to transmit Radio Frequency (RF) signals from the UAV beyond what might otherwise be needed because of various factors that might negatively influence the integrity of the RF link between the base station and the UAV. Such factors could be the changing attitude of the UAV as it flies, or possibly topographic obstructions, or even localized weather conditions (e.g., thunderstorms), that can be expected to significantly degrade the RF link between the UAV and the base station. For this reason, the transmit power used for the RF transmitter is set to a value that, during many times of use of the UAV, will be significantly more than what is needed. This factor limits the range of the UAV because excess electrical power from the UAV's on-board battery will be utilized by the on-board RF system during a given mission or operation.
The need to use extra power with an omnidirectional antenna on a UAV also gives rise to another, sometimes undesirable feature, and that is the detectability of the UAV (or interception of RF communications radiated from it) by other electronic detection systems. The use of an omnidirectional antenna broadcasts the RF signals transmitted by the UAV in an omnidirectional pattern that may facilitate radio-location of the vehicle and/or interception of communications.